Which thickness of aluminum filtration will most decrease the patient's skin dose?

• A. 1 mm.
• B. 0.5 mm.
• C. 2.5 mm.
• D. 2 mm.

Answer: (C)

Filtration works to remove the low-energy photons from the x-ray beam. Those low-energy photons contribute to patient skin dose but don’t help form the image, so removing them lowers the dose to the skin while still preserving enough high-energy photons to image well. The thicker the aluminum filter, the more low-energy photons are absorbed, and thus the greater the reduction in skin dose. Among the options, the 2.5 mm aluminum filtration is the thickest, so it provides the most decrease in skin dose. Keep in mind that increasing filtration also reduces beam intensity, so exposure settings may need adjustment to maintain proper image receptor exposure.